Gamma-Match formulas--design?
 

Anyone work with the gamma-match to the point of becomming a guru?
I am looking for "Everything you wanted to know about a gamma-match--in a
nutshell."
In other words, what set of formulas would give you length, conductor
spacing, gamma capacitor value, ratio of gamma rod to driven element
diameter, and a starting measurement for the shorting bar between
conductors-- for a given frequency?
What conditions requiring a match is the gamma best suited for?
What would need to be taken into consideration if one is using the match on
a monopole? A dipole (T-match version)? A driven element in a yagi? A
loop?

Regards
--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?

John Smith wrote:
In other words, what set of formulas would give you length, conductor
spacing, gamma capacitor value, ratio of gamma rod to driven element
diameter, and a starting measurement for the shorting bar between
conductors-- for a given frequency?

EZNEC will give you ballpark answers that require
some adjustments to length and capacitance. The
free version of EZNEC is available at www.eznec.com.

What conditions requiring a match is the gamma best suited for?

When your electrical dipole is one piece of metal,
i.e. a physical monopole. The center of 1/2WL of
one piece of metal has the voltage equal to zero
so you cannot feed it there but you can connect
ground to there. Then feed it some distance away
from center through a parallel element and a series
capacitor.
--
73, Cecil http://www.qsl.net/w5dxp

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I am sorry, I abbreviate my questions and think everyone psychic and will
know what I am thinking, it is a fault of mine, many have pointed it out to
me, I am working on correcting it (progress, as you can tell, has been
slow)... let me attempt to correct my error.

I am sure EZNEC is an excellent application. But with such applications,
you spend your time learning the application, rather than the underlying
principals; it requires you to structure yourself to fit the program. For
my hobby efforts with antennas, I would rather just learn and possess the
skills and do the calculations and design myself (I am rather eccentric this
way.)
Learning to rely on EZNEC I would just remain lazy and dependent on it and,
un-knowledgeable to the math workings and methods underneath it.

Since my son graduated college, I inherited his old "TI-83 Plus"
programmable graphing calculator. I was looking more for the actual
formulas and design methods to plug into the calculator--I would simply
translate them to basic language (maybe later assembly, its' a Z80
processor.)

The "Monopole" I had pictured in my mind was a 1/2 wave end-fed, but, I was
not sure if the gamma would even be suitable for this use--and I attempted
to leave my original question open-ended to catch this, if that was the
case.

I am glad you pointed out the center of a driven element, such as in a yagi,
is "dead" and can be attached directly to ground. If a 1/2 end-fed monopole
can be matched with gamma--would that still be the same case, only here the
"end" could be attached to a grounded mast?

Thank you for your reply, it is greatly appreciated.

Warmest regards,
John

--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Cecil Moore" wrote in message
...
John Smith wrote:
In other words, what set of formulas would give you length, conductor
spacing, gamma capacitor value, ratio of gamma rod to driven element
diameter, and a starting measurement for the shorting bar between
conductors-- for a given frequency?

EZNEC will give you ballpark answers that require
some adjustments to length and capacitance. The
free version of EZNEC is available at www.eznec.com.

What conditions requiring a match is the gamma best suited for?

When your electrical dipole is one piece of metal,
i.e. a physical monopole. The center of 1/2WL of
one piece of metal has the voltage equal to zero
so you cannot feed it there but you can connect
ground to there. Then feed it some distance away
from center through a parallel element and a series
capacitor.
--
73, Cecil http://www.qsl.net/w5dxp

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News==----
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Newsgroups
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John Smith wrote:
I am sure EZNEC is an excellent application. But with such applications,
you spend your time learning the application, rather than the underlying
principals;

I have learned many, many principles from using EZNEC which is
a really great learning tool. Look at it as reverse engineering.
You wonder why EZNEC reports such results and then you go discover
why. Modeling with ELNEC and EZNEC has taught me as much about
antennas as any other single source including Dr. Balanis' graduate
level college antenna course at ASU. One doesn't learn anything by
avoiding learning EZNEC. Dr. Balanis was amazed that an Intel
digital engineer already knew so much about antennas and I owe
that, in large part, to ELNEC and EZNEC.
--
73, Cecil http://www.qsl.net/w5dxp


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Yes, I am quite sure you are correct.

And, perhaps no one knows, or no one does it the old fashioned way and has
the formulas and steps at their disposal, I may have to seek other sources
than here.

However, I am a software engineer, once I understand the underlying math and
methods I can write such an application myself.

When the final drafts of these programs are released, antenna design, I am
sure you will just draw your antenna on virtual graph paper with ruled
lines, such as many of the draw programs have. And, be able to add any
inductance or capacitance just by selecting the point with the mouse, and
then entering values--the application will do everything else for you,
including making suggestions for improvement, matching, special conditions,
etc, etc--much like CAD (Computer Assisted Drafting) applications.

However, whether I use software, or simply divide 468/Fmhz, I still get a
half-wave.

It is fine if one wants to rely on software--I make my living on those who
do, I LOVE those people!--I just don't wish to invoke that method, later
when my understanding is absolute (well, greater than it is now) I may, or
write software specific to my needs...


Warmest regards
--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Cecil Moore" wrote in message
...
John Smith wrote:
I am sure EZNEC is an excellent application. But with such applications,
you spend your time learning the application, rather than the underlying
principals;

I have learned many, many principles from using EZNEC which is
a really great learning tool. Look at it as reverse engineering.
You wonder why EZNEC reports such results and then you go discover
why. Modeling with ELNEC and EZNEC has taught me as much about
antennas as any other single source including Dr. Balanis' graduate level
college antenna course at ASU. One doesn't learn anything by avoiding
learning EZNEC. Dr. Balanis was amazed that an Intel
digital engineer already knew so much about antennas and I owe
that, in large part, to ELNEC and EZNEC.
--
73, Cecil http://www.qsl.net/w5dxp


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet
News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000
Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

On Sun, 3 Apr 2005 08:17:48 -0700, "John Smith"
wrote:

I am looking for "Everything you wanted to know about a gamma-match--in a
nutshell."
In other words, what set of formulas would give you length, conductor
spacing, gamma capacitor value, ratio of gamma rod to driven element
diameter, and a starting measurement for the shorting bar between
conductors-- for a given frequency?

Hi Brett,

That question rather goes beyond the nutshell lead-in. However, for
the nutshell:
1/20th wave gamma rod;
capacitance about 5 to 8pF/Meter-of-wavelength;
gamma rod roughly half diameter as the radiator and spaced
roughly 1/100th wavelength from it.

With all the "roughlies" (a product of nutshell precision) it pays to
make the capacitor a variable, or the gamma loop length variable. All
such roughlies are also contingent upon the radiator's size WRT
wavelength.

To translate the capacitor characteristic:
for 20M band it would be 100 to 160pF

73's
Richard Clark, KB7QHC

Richard:

Thank you Sir!
This is information is exactly the type I was/am searching for.

Warmest regards,
John
--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Richard Clark" wrote in message
...
On Sun, 3 Apr 2005 08:17:48 -0700, "John Smith"
wrote:

I am looking for "Everything you wanted to know about a gamma-match--in a
nutshell."
In other words, what set of formulas would give you length, conductor
spacing, gamma capacitor value, ratio of gamma rod to driven element
diameter, and a starting measurement for the shorting bar between
conductors-- for a given frequency?

Hi Brett,

That question rather goes beyond the nutshell lead-in. However, for
the nutshell:
1/20th wave gamma rod;
capacitance about 5 to 8pF/Meter-of-wavelength;
gamma rod roughly half diameter as the radiator and spaced
roughly 1/100th wavelength from it.

With all the "roughlies" (a product of nutshell precision) it pays to
make the capacitor a variable, or the gamma loop length variable. All
such roughlies are also contingent upon the radiator's size WRT
wavelength.

To translate the capacitor characteristic:
for 20M band it would be 100 to 160pF

73's
Richard Clark, KB7QHC

John Smith wrote:
"In other words, what set of formulas would give you length, conductor
spacing, gamma capacitor value----?"

It looks experimental to me.

My ARRL Handbook says that the T match has an advantage in that a pair
of transmission line attachment points equidistant from the center of a
resonant wire has a resistance between them. Therefore it is possible to
choose points which match the line Zo. Problem is the physical distance
between the attachment points probably does not match the line spacing.
The handbook suggests a T match made like a folded dipole with
single-wire extensions at its ends. This looks as if it would require
experimentation.. It seems suited for parallel-wire lines.

The gamma match seems to be similar but an ubbalanced scheme where the
grounded line conductor is attached to the center of the radiator and
the ungrounded conductor is connected to the wire at a distance from the
center of the radiator which results in a low SWR on the transmission
line. A variation treats the gamma match as if it were a shunt tower
feed arangement.

The gamma match becomes a feed loop containing a ground path. The feed
loop is sized to that required for a resistive component which matches
the Zo of the transmission line. The loop inductively couples the
antenna with the transmission line. The loop`s reactance is always
inductive and can be tuned out with a series connected variable
capacitor.

It seems a good cut-and-try project to me. Maybe perfect for Art Unwin.

Best regards, Richard Harrison, KB5WZI

Dear John Smith (no call, no location)

Your questions contain assumptions. You assume that formulas amiable of
being programmed into a TI calculator exist for what it is you wish to do.
I doubt that they exist.

To borrow a term from your job, top-down is needed. Start with the
ARRL's Antenna Book. When you have digested its teachings, read either
Kraus' 3rd edition or Balanis' 2nd edition. Start at the beginning and
follow the road. It will be an interesting journey.
Regards, Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"John Smith" wrote in message
...
Yes, I am quite sure you are correct.

And, perhaps no one knows, or no one does it the old fashioned way and has
the formulas and steps at their disposal, I may have to seek other sources
than here.

However, I am a software engineer, once I understand the underlying math
and
methods I can write such an application myself.

When the final drafts of these programs are released, antenna design, I am
sure you will just draw your antenna on virtual graph paper with ruled
lines, such as many of the draw programs have. And, be able to add any
inductance or capacitance just by selecting the point with the mouse, and
then entering values--the application will do everything else for you,
including making suggestions for improvement, matching, special
conditions,
etc, etc--much like CAD (Computer Assisted Drafting) applications.

However, whether I use software, or simply divide 468/Fmhz, I still get a
half-wave.

It is fine if one wants to rely on software--I make my living on those who
do, I LOVE those people!--I just don't wish to invoke that method, later
when my understanding is absolute (well, greater than it is now) I may, or
write software specific to my needs...


Warmest regards



"Cecil Moore" wrote in message
...
John Smith wrote:
I am sure EZNEC is an excellent application. But with such
applications,
you spend your time learning the application, rather than the
underlying
principals;

I have learned many, many principles from using EZNEC which is
a really great learning tool. Look at it as reverse engineering.
You wonder why EZNEC reports such results and then you go discover
why. Modeling with ELNEC and EZNEC has taught me as much about
antennas as any other single source including Dr. Balanis' graduate
level
college antenna course at ASU. One doesn't learn anything by avoiding
learning EZNEC. Dr. Balanis was amazed that an Intel
digital engineer already knew so much about antennas and I owe
that, in large part, to ELNEC and EZNEC.
--
73, Cecil http://www.qsl.net/w5dxp

ok...
I cut a 1/2 wave monopole for 28.4Mhz and used the dimensions according to
what you stated. The capacitor is homebrew from 3/16 acrylic sheet with
aluminum plates, configured as a compression variable, true pf is unknown
(with spacing and dielectric of acrylic and size of plates, should max at
~150 pf) --but plenty of adjustment, both sides of "null" on swr meter.

However, the shorting bar on the gamma rod had to be raised to ~3 ft.
(adjustment above or below this height only increases swr), here the swr is
~1.7:1. I cannot find a configuration on the gamma which brings the swr
under that figure... lengthing/shorting monopole +2 to -2 inches has
negligible effect and not for the better.

Lenght of coax from rf source to ant seems critical, when coax is shortened
or lengthened, gamma must be adjusted (but is always around 3 ft)

The gamma rod length seems to be quite above what the figures you gave me
would suggest (from what you suggested, 1/20 wave (~20 inches or do I have
that correct?)--what am I too blind to see to see here, or what I am I
ignorant of?

Your continued help and advice would be most appreciated...

Warmest regards,
John
--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Richard Clark" wrote in message
...
On Sun, 3 Apr 2005 08:17:48 -0700, "John Smith"
wrote:

I am looking for "Everything you wanted to know about a gamma-match--in a
nutshell."
In other words, what set of formulas would give you length, conductor
spacing, gamma capacitor value, ratio of gamma rod to driven element
diameter, and a starting measurement for the shorting bar between
conductors-- for a given frequency?

Hi Brett,

That question rather goes beyond the nutshell lead-in. However, for
the nutshell:
1/20th wave gamma rod;
capacitance about 5 to 8pF/Meter-of-wavelength;
gamma rod roughly half diameter as the radiator and spaced
roughly 1/100th wavelength from it.

With all the "roughlies" (a product of nutshell precision) it pays to
make the capacitor a variable, or the gamma loop length variable. All
such roughlies are also contingent upon the radiator's size WRT
wavelength.

To translate the capacitor characteristic:
for 20M band it would be 100 to 160pF

73's
Richard Clark, KB7QHC